Registration method, session establishment method, terminal, and AMF entity

ABSTRACT

A registration method, a session establishment method, a terminal, and an access and mobility management function (AMF) entity, where the method includes: sending, by a terminal, a first message to the AMF entity, where the first message includes first information, first network slice selection information, and second network slice selection information, the first information includes information for requesting to establish a protocol data unit (PDU) session, the first network slice selection information is used by the AMF entity to select a first session management function (SMF) entity, and the second network slice selection information is used by the AMF entity to select a second SMF entity; and receiving, by the terminal, a second message from the AMF entity, where the second message includes second information, and the second information includes PDU session establishment accept information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/557,193, filed on Aug. 30, 2019, which is a continuation of U.S.patent application Ser. No. 16/314,180, filed on Dec. 28, 2018, now U.S.Pat. No. 10,425,987, which is a national stage of International PatentApplication No. PCT/CN2017/089016, filed on Jun. 19, 2017. All of theaforementioned applications are hereby incorporated by reference intheir entireties.

TECHNICAL FIELD

Embodiments of this application relate to the field of communicationstechnologies, and in particular, to a registration method for aterminal, a session establishment method, a terminal, and an access andmobility management function (AMF) entity.

BACKGROUND

As communications technologies develop and a requirement of a user on acommunications network is ever-increasing, a 5^(th) generation (5G)communications network technology (or referred to as 5th generationmobile communications technology) is being rapidly standardized. Alogical concept of a network slice is introduced in the 5Gcommunications network technology. An operator pre-configures a networkslice selection policy (NSSP) for a terminal. It should be noted that,the terminal may also be referred to as a user equipment (UE). Thepre-configured NSSP includes one or more rules, and each rule associatesa third-party application program (App) to single network sliceselection assistance information (S-NSSAI). When the UE needs to use anapp, the UE obtains corresponding S-NSSAI through mapping based on therule in the NSSP, and establishes a protocol data unit (PDU) session ina network slice corresponding to the S-NSSAI.

However, a case in which an NSSP in a visited public land mobile network(VPLMN) is not configured for the UE may exist. When the UE roams to theVPLMN, the UE has no NSSP in the VPLMN, and consequently cannotdetermine a network slice in which a PDU session established.Alternatively, the following case may exist: When the UE roams to aVPLMN, the UE obtains an NSSP in the VPLMN, but when the UE needs to usean app of a home public land mobile network (HPLMN), the UE cannot finda corresponding rule from the NSSP in the VPLMN, and consequently the UEcannot determine to-be-used S-NSSAI to establish a PDU session.

SUMMARY

Embodiments of this application provide a registration method for aterminal, a session establishment method, a terminal, and an AMF entitysuch that the terminal obtains an NSSP in a VPLMN or an HPLMN in whichthe terminal is located, to accurately determine S-NSSAI in the VPLMN orthe HPLMN in a PDU session establishment process, and complete PDUsession establishment.

According to a first aspect, an embodiment of this application providesa registration method for a terminal, where the registration methodincludes: sending, by a terminal, a registration request message to anaccess and mobility management function (AMF) entity, where theregistration request message includes a first parameter such as needNSSP indication information, and the first parameter is used to requesta network slice selection policy; and receiving, by the terminal, aregistration accept message sent by the AMF entity, where theregistration accept message includes the network slice selection policysuch that in a process in which the terminal subsequently establishes aPDU session, the terminal can accurately determine corresponding S-NSSAIbased on an NSSP in a current VPLMN or an NSSP in a current HPLMN, andthe following case is avoided: When the terminal establishes a PDUsession, the AMF entity cannot find S-NSSAI corresponding to a networkin which the terminal is located, and cannot complete PDU sessionestablishment, and consequently the terminal cannot performcommunication.

According to a second aspect, an embodiment of this application providesa session establishment method, where the method may include: sending,by a terminal, a first message to an AMF entity, where the first messageincludes first information, first network slice selection information,and second network slice selection information, the first informationincludes information for requesting to establish a PDU session, thefirst network slice selection information is used by the AMF entity toselect a first session management function (SMF) entity, and the secondnetwork slice selection information is used by the AMF entity to selecta second SMF entity such that in a PDU session establishment process,the AMF entity accurately determines S-NSSAI, and completes PDU sessionestablishment; and receiving, by the terminal, a second message sent bythe AMF entity, where the second message includes second information,and the second information includes PDU session establishment acceptinformation.

In an implementation, the first network slice selection information issingle network slice selection assistance information (S-NSSAI)corresponding to a first application in a visited public land mobilenetwork (VPLMN), and the second network slice selection information isS-NSSAI corresponding to the first application in a home public landmobile network (HPLMN).

Optionally, in another implementation, the first message furtherincludes indication information, where the indication information isused to indicate that the first network slice selection information isS-NSSAI in a VPLMN, or the indication information is used to indicatethat the first network slice selection information is S-NSSAI in aHPLMN.

According to a third aspect, an embodiment of this application providesa session establishment method, where the method includes: sending, by aterminal, a first message to an AMF entity, where the first messageincludes first information, network slice selection information, andindication information, the first information includes information forrequesting to establish a PDU session, the network slice selectioninformation is used by the AMF entity to select an SMF entity, and theindication information is used to indicate that the network sliceselection information is S-NSSAI in a VPLMN, or is used to indicate thatthe network slice selection information is S-NSSAI in a HPLMN such thatin a PDU session establishment process, the AMF entity accuratelydetermines S-NSSAI, and completes PDU session establishment; andreceiving, by the terminal, a second message sent by the AMF entity,where the second message includes second information, and the secondinformation includes PDU session establishment accept information.

In a possible implementation, the network slice selection information isS-NSSAI corresponding to a first application.

Optionally, in another possible implementation, before the sending, by auser equipment, a first message to an AMF entity, the method may furtherinclude: determining, by the terminal, the network slice selectioninformation.

In a possible implementation, the determining, by the terminal, thenetwork slice selection information includes: if S-NSSAI correspondingto the first application exists in a network slice selection policy inthe VPLMN, determining, by the terminal, the S-NSSAI as the networkslice selection information; or if S-NSSAI corresponding to the firstapplication exists in a network slice selection policy in the HPLMN,determining, by the terminal, the S-NSSAI as the network slice selectioninformation.

In the embodiments of this application, the session establishment methodprovided in the second aspect and the session establishment methodprovided in the third aspect may be implemented on a basis of theregistration method provided in the first aspect.

According to a fourth aspect, an embodiment of this application providesa registration method, where the method may include: receiving, by anAMF entity, a registration request message sent by a terminal, where theregistration request message includes a first parameter, and the firstparameter is used to request a network slice selection policy;obtaining, by the AMF, a network slice selection policy based on theregistration request message; and sending, by the AMF, a registrationaccept message to the terminal, where the registration accept messageincludes the network slice selection policy.

After the solution provided in this embodiment of this application isused, in a PDU session establishment process, the terminal canaccurately determine S-NSSAI based on an NSSP in a VPLMN or an HPLMN inwhich the terminal is currently located, to complete PDU sessionestablishment.

Optionally, in a possible implementation, the obtaining, by the AMFentity, a network slice selection policy based on the registrationrequest message may include: sending, by the AMF entity, a first messageto a policy control function (PCF) entity, where the first messageincludes the first parameter; and receiving, by the AMF entity, a secondmessage sent by the PCF entity, where the second message includes thenetwork slice selection policy.

According to a fifth aspect, an embodiment of this application providesa session establishment method, where the method includes: receiving, byan AMF entity, a first message sent by a terminal, where the firstmessage includes first information, first network slice selectioninformation, and second network slice selection information, and thefirst information includes information for requesting to establish a PDUsession; determining, by the AMF entity, a first SMF entity based on thefirst network slice selection information, and determining a second SMFentity based on the second network slice selection information; andsending, by the AMF entity, a second message to the terminal, where thesecond message includes second information, and the second informationincludes PDU session establishment accept information.

After the solution provided in this embodiment of this application isused, the AMF entity can accurately determine corresponding S-NSSAIbased on the message that is sent by the terminal and that includes thefirst network slice selection information and the second network sliceselection information, to complete PDU session establishment.

Optionally, in a possible implementation, the first network sliceselection information is S-NSSAI corresponding to a first application ina VPLMN; and the second network slice selection information is S-NSSAIcorresponding to the first application in a HPLMN.

Optionally, in another possible implementation, the first messagefurther includes indication information, where the indicationinformation is used to indicate that the first network slice selectioninformation is S-NSSAI in a VPLMN, or the indication information is usedto indicate that the first network slice selection information isS-NSSAI in a HPLMN.

According to a sixth aspect, an embodiment of this application providesa session establishment method, where the method includes: receiving, byan AMF entity, a first message sent by a terminal, where the firstmessage includes first information, first network slice selectioninformation, and indication information, the first information includesinformation for requesting to establish a PDU session, and theindication information is used to indicate that the first network sliceselection information is S-NSSAI in a VPLMN, or is used to indicate thatthe network slice selection information is S-NSSAI in a HPLMN;determining, by the AMF based on the indication information, that thefirst network slice selection information is the S-NSSAI in the VPLMN orthe first network slice selection information is the S-NSSAI in theHPLMN, selecting a first SMF entity based on the first network sliceselection information, determining second network slice selectioninformation based on the first network slice selection information andinformation about a correspondence between VPLMN S-NSSAI and HPLMNS-NSSAI, and selecting a second SMF entity based on the second networkslice selection information; and sending, by the AMF entity, a secondmessage to the terminal, where the second message includes secondinformation, and the second information includes PDU sessionestablishment accept information.

After the solution provided in this embodiment of this application isused, the AMF entity can accurately determine to-be-used S-NSSAI basedon the first network slice selection information and the indicationinformation, to complete PDU session establishment.

Optionally, in a possible implementation, the first network sliceselection information is S-NSSAI corresponding to a first application.

In the embodiments of this application, the session establishment methodprovided in the fifth aspect and the session establishment methodprovided in the sixth aspect may be implemented on a basis of theregistration method provided in the fourth aspect.

According to a seventh aspect, an embodiment of this applicationprovides a terminal, where the terminal includes a sending unit and areceiving unit that are configured to complete the method/steps in thefirst aspect. In addition, the terminal may further include a processingunit and a storage unit, where the processing unit is configured toprocess related data, and the storage unit is configured to store arelated instruction and related data.

According to an eighth aspect, an embodiment of this applicationprovides a terminal, where the terminal includes a sending unit and areceiving unit that are configured to complete the method/steps in anyone of the second aspect or the possible implementations of the secondaspect. In addition, the terminal may further include a processing unitand a storage unit, where the processing unit is configured to processrelated data, and the storage unit is configured to store a relatedinstruction and related data.

According to a ninth aspect, an embodiment of this application providesa terminal, where the terminal includes a sending unit, a receivingunit, and a processing unit that are configured to complete themethod/steps in any one of the third aspect or the possibleimplementations of the third aspect. In addition, the terminal mayfurther include a storage unit, where the storage unit is configured tostore a related instruction and related data.

According to a tenth aspect, an embodiment of this application providesan access and mobility management function entity, where the access andmobility management function entity includes a receiving unit, aprocessing unit, and a sending unit that are configured to complete themethod/steps in any one of the fourth aspect or the possibleimplementations of the fourth aspect. In addition, the access andmobility management function entity may further include a storage unit,where the storage unit is configured to store a related instruction andrelated data.

According to an eleventh aspect, an embodiment of this applicationprovides an access and mobility management function entity, where theaccess and mobility management function entity includes a receivingunit, a processing unit, and a sending unit that are configured tocomplete the method/steps in any one of the fifth aspect or the possibleimplementations of the fifth aspect. In addition, the access andmobility management function entity may further include a storage unit,where the storage unit is configured to store a related instruction andrelated data.

According to a twelfth aspect, an embodiment of this applicationprovides an access and mobility management function entity, where theaccess and mobility management function entity includes a receivingunit, a processing unit, and a sending unit that are configured tocomplete the method/steps in any one of the sixth aspect or the possibleimplementations of the sixth aspect. In addition, the access andmobility management function entity may further include a storage unit,where the storage unit is configured to store a related instruction andrelated data.

According to a thirteenth aspect, an embodiment of this applicationprovides a terminal, where the terminal includes: a transmitterconfigured to send a registration request message to an AMF entity,where the registration request message includes a first parameter, andthe first parameter is used to request a network slice selection policy;and a receiver configured to receive a registration accept message sentby the AMF entity, where the registration accept message includes thenetwork slice selection policy such that in a process in which theterminal subsequently establishes a PDU session, the terminal canaccurately determine corresponding S-NSSAI based on an NSSP in a currentVPLMN or HPLMN, and the following case is avoided: When the terminalestablishes a PDU session, the AMF entity cannot find S-NSSAIcorresponding to a network in which the terminal is located, and cannotcomplete PDU session establishment, and consequently the terminal cannotperform communication.

According to a fourteenth aspect, an embodiment of this applicationprovides a terminal, where the terminal includes: a transmitterconfigured to send a first message to an AMF entity, where the firstmessage includes first information, first network slice selectioninformation, and second network slice selection information, the firstinformation includes information for requesting to establish a PDUsession, the first network slice selection information is used by theAMF entity to select a first SMF entity, and the second network sliceselection information is used by the AMF entity to select a second SMFentity; and a receiver configured to receive a second message sent bythe AMF entity, where the second message includes second information,and the second information includes PDU session establishment acceptinformation.

After the terminal provided in this embodiment of this application isused, in a PDU session establishment process, the AMF entity canaccurately determine S-NSSAI, to complete PDU session establishment. Thefollowing case is avoided: When the terminal establishes a PDU session,the AMF entity cannot find S-NSSAI corresponding to a network in whichthe terminal is located, and cannot complete PDU session establishment,and consequently the terminal cannot perform communication.

Optionally, in a possible implementation, the first network sliceselection information is S-NSSAI corresponding to a first application ina VPLMN, and the second network slice selection information is S-NSSAIcorresponding to the first application in a HPLMN.

Optionally, in another possible implementation, the first messagefurther includes indication information, where the indicationinformation is used to indicate that the first network slice selectioninformation is S-NSSAI in a VPLMN, or the indication information is usedto indicate that the first network slice selection information isS-NSSAI in a HPLMN.

According to a fifteenth aspect, an embodiment of this applicationprovides a terminal, where the terminal may include: a transmitterconfigured to send a first message to an AMF entity, where the firstmessage includes first information, network slice selection information,and indication information, the first information includes informationfor requesting to establish a PDU session, the network slice selectioninformation is used by the AMF entity to select an SMF entity, and theindication information is used to indicate that the network sliceselection information is S-NSSAI in a VPLMN, or is used to indicate thatthe network slice selection information is S-NSSAI in a HPLMN; and areceiver configured to receive a second message sent by the AMF entity,where the second message includes second information, and the secondinformation includes PDU session establishment accept information.

After the terminal provided in this embodiment of this application isused, in a PDU session establishment process, the AMF entity canaccurately determine S-NSSAI, to complete PDU session establishment. Thefollowing case is avoided: When the terminal establishes a PDU session,the AMF entity cannot find S-NSSAI corresponding to a network in whichthe terminal is located, and cannot complete PDU session establishment,and consequently the terminal cannot perform communication.

Optionally, in a possible implementation, the network slice selectioninformation is S-NSSAI corresponding to a first application.

Optionally, in another possible implementation, the terminal furtherincludes a processor configured to determine the network slice selectioninformation.

Optionally, in a possible implementation, that the processor determinesthe network slice selection information includes: if S-NSSAIcorresponding to the first application exists in a network sliceselection policy in the VPLMN, determining, by the terminal, the S-NSSAIas the network slice selection information; or if S-NSSAI correspondingto the first application exists in a network slice selection policy inthe HPLMN, determining, by the terminal, the S-NSSAI as the networkslice selection information.

According to a sixteenth aspect, an embodiment of this applicationprovides an AMF entity, where the AMF entity includes: a receiverconfigured to receive a registration request message sent by a terminal,where the registration request message includes a first parameter, andthe first parameter is used to request a network slice selection policy;a processor configured to obtain a network slice selection policy basedon the registration request message; and a transmitter configured tosend a registration accept message to the terminal, where theregistration accept message includes the network slice selection policy.

A network slice selection policy in a network in which the terminal islocated is obtained using the first parameter sent by the terminal tothe AMF entity such that when a PDU session is subsequently established,corresponding S-NSSAI is accurately determined based on the networkslice selection policy, and the following case is avoided: When theterminal establishes a PDU session, the AMF entity cannot find S-NSSAIcorresponding to the network in which the terminal is located, andcannot complete PDU session establishment, and consequently the terminalcannot perform communication.

Optionally, in a possible implementation, that the processor obtains anetwork slice selection policy based on the registration request messageincludes: sending, by the transmitter, a first message to a PCF entity,where the first message includes the first parameter; and receiving, bythe receiver, a second message sent by the PCF entity, where the secondmessage includes the network slice selection policy.

According to a seventeenth aspect, an embodiment of this applicationprovides an AMF entity, where the AMF entity includes: a receiverconfigured to receive a first message sent by a terminal, where thefirst message includes first information, first network slice selectioninformation, and second network slice selection information, and thefirst information includes information for requesting to establish a PDUsession; a processor configured to determine a first SMF entity based onthe first network slice selection information, and determine a secondSMF entity based on the second network slice selection information; anda transmitter configured to send a second message to the terminal, wherethe second message includes second information, and the secondinformation includes PDU session establishment accept information.

Therefore, in a process in which the terminal subsequently establishes aPDU session, the terminal can accurately determine corresponding S-NSSAIbased on an NSSP in a current VPLMN or HPLMN, and the following case isavoided: When the terminal establishes a PDU session, the AMF entitycannot find S-NSSAI corresponding to a network in which the terminal islocated, and cannot complete PDU session establishment, and consequentlythe terminal cannot perform communication.

Optionally, in a possible implementation, the first network sliceselection information is S-NSSAI corresponding to a first application ina VPLMN; and the second network slice selection information is S-NSSAIcorresponding to the first application in a HPLMN.

In another possible implementation, the first message further includesindication information, where the indication information is used toindicate that the first network slice selection information is S-NSSAIin a VPLMN, or the indication information is used to indicate that thefirst network slice selection information is S-NSSAI in a HPLMN.

According to an eighteenth aspect, an embodiment of this applicationprovides an AMF entity, where the AMF entity includes: a receiverconfigured to receive a first message sent by a terminal, where thefirst message includes first information, first network slice selectioninformation, and indication information, the first information includesinformation for requesting to establish a PDU session, and theindication information is used to indicate that the first network sliceselection information is S-NSSAI in a VPLMN, or is used to indicate thatthe network slice selection information is S-NSSAI in a HPLMN.Additionally, the AMF entity includes a processor configured to:determine, based on the indication information, that the first networkslice selection information is the S-NSSAI in the VPLMN or the firstnetwork slice selection information is the S-NSSAI in the HPLMN; selecta first SMF entity based on the first network slice selectioninformation; determine second network slice selection information basedon the first network slice selection information and information about acorrespondence between VPLMN S-NSSAI and HPLMN S-NSSAI; and select asecond SMF entity based on the second network slice selectioninformation. The AMF entity further includes a transmitter configured tosend a second message to the terminal, where the second message includessecond information, and the second information includes PDU sessionestablishment accept information.

After the solution provided in this embodiment of this application isused, the AMF entity can accurately determine to-be-used S-NSSAI basedon the first network slice selection information and the indicationinformation, to complete PDU session establishment.

In a possible implementation, the first network slice selectioninformation is S-NSSAI corresponding to a first application.

According to a nineteenth aspect, an embodiment of this applicationprovides a computer program product including an instruction, and whenthe instruction runs on a computer, the method/steps in any one of thefirst to the sixth aspect or the possible implementations thereof is/areperformed.

According to a twentieth aspect, an embodiment of this applicationprovides a computer readable storage medium configured to store aninstruction, and when the instruction is executed on a computer, themethod/steps in any one of the first to the sixth aspect or the possibleimplementations thereof is/are performed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a network architecture in which the 3rdGeneration Partnership Project (3GPP) supports a plurality of networkslices according to an embodiment of this application;

FIG. 2 is a schematic structural diagram of a core network in a 5Gcommunications network according to an embodiment of this application;

FIG. 3 is a schematic diagram of a network architecture of a localbreakout scenario according to an embodiment of this application;

FIG. 4 is a schematic diagram of a network architecture of a home routedscenario according to an embodiment of this application;

FIG. 5 is a flowchart in which user equipment performs registrationaccording to an embodiment of this application;

FIG. 6A and FIG. 6B are flowcharts of a session establishment methodaccording to an embodiment of this application;

FIG. 7A and FIG. 7B are flowcharts of another session establishmentmethod according to an embodiment of this application;

FIG. 8A and FIG. 8B are flowcharts of still another sessionestablishment method according to an embodiment of this application;

FIG. 9 is a schematic structural diagram of a terminal according to anembodiment of this application;

FIG. 10 is a schematic structural diagram of another terminal accordingto an embodiment of this application;

FIG. 11 is a schematic structural diagram of still another terminalaccording to an embodiment of this application;

FIG. 12 is a schematic structural diagram of an access and mobilitymanagement function entity according to an embodiment of thisapplication;

FIG. 13 is a schematic structural diagram of another access and mobilitymanagement function entity according to an embodiment of thisapplication;

FIG. 14 is a schematic structural diagram of still another access andmobility management function entity according to an embodiment of thisapplication;

FIG. 15 is a schematic structural diagram of a terminal according to anembodiment of this application;

FIG. 16 is a schematic structural diagram of another terminal accordingto an embodiment of this application;

FIG. 17 is a schematic structural diagram of still another terminalaccording to an embodiment of this application;

FIG. 18 is a schematic structural diagram of an access and mobilitymanagement function entity according to an embodiment of thisapplication;

FIG. 19 is a schematic structural diagram of another access and mobilitymanagement function entity according to an embodiment of thisapplication; and

FIG. 20 is a schematic structural diagram of still another access andmobility management function entity according to an embodiment of thisapplication.

DESCRIPTION OF EMBODIMENTS

The following describes the embodiments of this application withreference to the accompanying drawings in the embodiments of thisapplication.

The embodiments of this application provide a registration method, asession establishment method, a terminal, and an AMF entity that areapplied to a 5G communications network. A logical concept of a networkslice and a structure of the network slice are introduced in a corenetwork in the 5G communications network.

A network slice is a set of logical network function entities thatsupport a particular communication service requirement, and mainlyimplements a customizable service for a communication service using asoftware-defined networking (SND) technology and a Network FunctionsVirtualization (NFV) technology. The logical network function entitymentioned herein may include an AMF entity, an SMF entity, and a userplane function (UPF) entity that are mentioned below. For details, referto descriptions in FIG. 2 .

The NFV technology may implement mapping of an underlying physicalresource into a virtualization resource, construction of a virtualmachine, and loading of a network function (NF). The SDN technology mayimplement a logical connection between virtual machines and constructionof channels for bearer signaling and a data flow. The network slicefinally implements a dynamic connection between network functionentities in a radio access network (RAN) and the core network (CN),configures an end-to-end service chain, and implements flexiblenetworking, to implement a customizable network service. An operator maydetermine a network slice based on a requirement of each specificcommunication service on a key performance indicator (KPI) such as acapacity, coverage, a speed, and a latency, and the network sliceincludes a set of network function entities, to provide a requiredtelecommunication service and network capability service for a user, andmeet a particular market scenario and requirement.

As shown in FIG. 1 , FIG. 1 is a schematic diagram of a networkarchitecture in which the 3rd Generation Partnership Project (3GPP)supports a plurality of network slices. The 3GPP classifies a 5G networkslice into the following three main types: a network slice of anenhanced mobile broadband (eMBB) service type, a network slice of amassive Internet of Things (mIoT) service type, a network slice of anultra-reliable and low latency communications (URLLC) service type, amultimedia device, and the like. The network slice of the mIoT type ismainly for a terminal in the Internet of Things, and the terminal has arequirement on massiveness, low mobility, and a relatively low speed.The network slice of the URLLC type is mainly for a terminal in theInternet of Vehicles, and the terminal has a relatively high requirementon a latency and reliability. For example, a mobile phone may access thenetwork slice of the eMBB type for high-speed downloading and 4Khigh-definition video viewing, and a sensor device may access thenetwork slice of an mMTC type for small data transmission and systemconfiguration update.

To enable one terminal to support a plurality of communication servicesto improve user experience, one terminal is allowed to access one ormore network slices, and technical solutions in the embodiments of thisapplication are applicable to a scenario in which one terminal accessesone or more network slices.

To be more specific, each network slice provides a particular servicefor a particular terminal. The terminal in the embodiments of thisapplication may also be referred to as a UE, and may be a device thatprovides voice and/or data connectivity for a user, a handheld devicewith a wireless connection function, or another processing deviceconnected to a wireless modem. The wireless terminal may communicatewith one or more core networks using a RAN. The wireless terminal may bea mobile terminal, such as a mobile phone (or referred to as a“cellular” phone) and a computer with a mobile terminal device. Forexample, the wireless terminal may be a portable, pocket-sized,handheld, computer built-in, or in-vehicle mobile apparatus thatexchanges voice and/or data with the radio access network. For example,the wireless terminal may be a device such as a personal communicationsservice (PCS) phone, a cordless telephone set, a Session InitiationProtocol (SIP) phone, a wireless local loop (WLL) station, or a personaldigital assistant (PDA). The wireless terminal may also be referred toas a system, a subscriber unit, a subscriber station, a mobile station,a mobile, a remote station, an access point, a remote terminal, anaccess terminal, a user terminal, a user agent, a user device, or user aequipment. This is not limited in the embodiments of this application.Based on a service type, the UE in the embodiments of the presentdisclosure may be the foregoing terminal device that has a relativelyhigh requirement on a speed and mobility, for example, a mobile phone ora multimedia device, or may be a terminal in the Internet of Things, ormay be a terminal in the Internet of Vehicles.

A network slice is implemented as a network slice instance (NSI) duringnetwork deployment. One network slice may be implemented as a pluralityof network slice instances.

One UE may use a plurality of NSIs, and the NSIs may share a RAN deviceand an AMF entity, but a session management function (SMF) entity and auser plane function (UPF) entity are network elements unique to the NSI.As shown in FIG. 2 , FIG. 2 is a schematic structural diagram of a corenetwork in a 5G communications network according to an embodiment ofthis application.

In the embodiments of this application, the AMF entity, the SMF entity,and the UPF entity may be one or more servers in the core network.

The AMF entity has functions such as mobility management, registrationmanagement, and connection management for the UE, lawful interception,transmission of session management (SM) information between the UE andthe SMF entity, access authentication, and access authorization.

The SMF entity has functions such as session management and roaming. Thesession management function is, for example, session establishment,modification, and release, and includes maintenance of a tunnel betweenthe UPF and an access network (AN) node. The roaming function mayinclude charging data collection, and transmission of signaling forauthentication/authorization with an external data network (DN).

The UPF entity has functions such as packet routing and lawfulinterception.

In FIG. 2 , one UE may use two network slice instances NSI1 and NSI2.The NSI1 and the NSI2 share a RAN device and an AMF entity. An SMF1entity and a UPF1 entity are network elements unique to the NSI1, and anSMF2 entity and a UPF2 entity are network elements unique to the NSI2.The UPF1 entity and the UPF2 entity are respectively connected to acorresponding data network 1 and data network 2.

The UE is connected to the RAN using a Uu interface. Data between theRAN and UPF1 entity and that between the RAN and UPF2 entity aretransmitted using an N3 interface. Signaling and data between the RANdevice and the AMF entity are transmitted using an N2 interface.Signaling and data between the AMF entity and the SMF1 entity and thosebetween the AMF entity and the SMF2 entity are transmitted using an N11interface. Signaling and data between the SMF1 entity and the UPF1entity and those between the SMF1 entity and the UPF1 entity aretransmitted using N4. It should be noted that, the Uu interface, the N2interface, the N3 interface, the N11 interface, and the N4 interface arealready defined in a standard.

When the UE roams to a VPLMN, based on a network decision and UEsubscription, a roaming scenario may fall into two types: home routedand local breakout. Network architectures of the two scenarios are shownin FIG. 3 and FIG. 4 .

FIG. 3 is a schematic diagram of a network architecture of a localbreakout scenario according to an embodiment of this application. FIG. 4is a schematic diagram of a network architecture of a home routedscenario according to an embodiment of this application.

When the UE initiates a PDU session establishment request, the AMFentity first selects a network slice NSI based on S-NSSAI reported bythe UE, and then selects unique network elements, namely, an SMF entityand a UPF entity, corresponding to the network slice NSI.

As shown in FIG. 3 , the network architecture is a network architectureof the local breakout scenario. In the local breakout scenario, a UEroams to a VPLMN and initiates a PDU session establishment request. AnAMF entity in the VPLMN, that is referred to as a V-AMF entity, firstselects a network slice V-NSI1 in the VPLMN based on S-NSSAI reported bythe UE, and then selects unique network elements, namely, a V-SMF entityand a V-UPF entity, corresponding to the V-NSI1. This process is similarto that in a non-roaming case. The V-SMF entity is an SMF entity in theVPLMN in which the UE is located, and the V-UPF entity is a UPF entityin the VPLMN in which the UE is located.

As shown in FIG. 4 , the network architecture is a network architectureof the home routed scenario. In the home routed scenario, a UE roams toa VPLMN, and the UE uses a V-NSI1. The V-NSI1 includes a V-RAN device, aV-AMF entity, and unique network elements: a V-SMF1 entity and a V-UPF1entity. The UE uses an H-NSI2 in a home network, and network elementsunique to the H-NSI2 are an H-SMF2 entity and an H-UPF2 entity.

When the UE initiates a PDU session establishment request, the V-AMFselects a V-SMF entity based on S-NSSAI in the VPLMN, and selects anH-SMF entity based on S-NSSAI in an HPLMN. The V-SMF entity and theH-SMF entity respectively select a V-UPF entity and an H-UPF entity.Uplink data transmission is: UE→RAN device→V-UPF entity→H-UPF entity,and downlink data transmission is opposite to the uplink datatransmission.

With reference to the accompanying drawings, the following describes thesession establishment method provided in the embodiments of thisapplication. It should be noted that, the AMF entity mentioned below isthe V-AMF entity in the VPLMN, unless otherwise stated.

When a UE roams from a home network to a VPLMN, the UE first needs toperform network registration. A network registration process is shown inFIG. 5 , and the process may include the following steps.

S110. The UE sends a registration request message to an AMF entity.

The registration request message includes a first parameter, and thefirst parameter is used to request a network slice selection policy. Inthis embodiment of this application, the first parameter may be needNSSP indication information, and is used to request an NSSP from the AMFentity.

The registration request message may further include an identifier ofthe UE. The identifier of the UE may be a temporary identifier, namely,an identifier that is temporarily allocated to the UE, for example, aglobally unique temporary UE identity (GUTI). In this embodiment of thisapplication, the identifier may be an identifier that is allocated bythe AMF entity to the UE during previous registration of the UE.

S120. The AMF entity obtains an NSSP from a policy control function(PCF) entity based on the registration request message.

The AMF entity obtains the network slice selection policy (NSSP) fromthe PCF entity based on the identifier such as the GUTI of the UE andthe first parameter that are in the registration request message.

The PCF entity is a logical function device, may be one or more servers,and is configured to provide a policy for a control-plane entity or theUE, namely, the PCF entity is configured to perform policy managementand control.

A process in which the AMF obtains the NSSP from the PCF entity may besteps S121 and S122 that are shown in FIG. 5 .

S121. The AMF entity sends a user equipment context establishmentrequest message to the PCF entity.

The user equipment context establishment request message includes thefirst parameter and an identifier of the UE. The identifier of the UEmay be a subscription permanent identifier (SUPI), and the SUPI mayinclude an international mobile subscriber identity (IMSI), a networkaccess identifier (NAI), and the like. The identifier SUPI of the UE isdetermined by the AMF entity based on the identifier GUTI of the UE. Forexample, if the SUPI of the UE is an IMSI, the AMF entity determines theidentifier IMSI of the UE based on the identifier GUTI of the UE andinformation that is about a relationship between an identifier GUTI andan identifier IMSI of UE and that is stored in the AMF entity. In otherwords, the permanent identifier IMSI of the UE can be found based on thetemporary identifier GUTI of the UE.

S122. The AMF entity receives a UE context establishment responsemessage sent by the PCF entity.

After receiving the user context establishment request message sent bythe AMF entity, the PCF entity establishes context of the UE in the PCFentity based on the IMSI of the UE, and sends the user contextestablishment response message to the AMF entity based on the need NSSPindication information. The user context establishment response messageincludes the SUPI of the UE and the NSSP of the UE.

After receiving the UE context establishment response message, the AMFentity performs step S130.

S130. The AMF entity sends a registration accept message to the UE.

The registration accept includes the NSSP such that the UE obtains theNSSP in a currently registered VPLMN. Compared with other approaches,the UE may obtain, from the AMF entity, the NSSP in the currentlyregistered VPLMN, instead of obtaining a mapping relationship betweenHPLMN NSSAI and VPLMN NSSAI from the AMF entity. When obtaining the NSSPin the VPLMN, the UE may accurately determine, based on the NSSP,S-NSSAI that should be used for an app in the current VPLMN.

Optionally, as shown in FIG. 5 , in this embodiment of this application,after the AMF entity receives the registration request message sent bythe UE, the method may further include the following steps.

S140. The AMF entity sends update location information to a user datamanagement (UDM) entity.

The UDM entity may be a server, and is configured to manage user data,for example, location management and subscription management.

The AMF entity determines an IMSI of the UE based on the GUTI of the UEin the received registration request message, and sends the updatelocation information to the UDM. The UDM receives the update locationinformation sent by the AMF, updates the current AMF entity of the UEbased on the SUPI of the UE, and sends an update locationacknowledgement (ACK) message to the AMF entity.

S150. The AMF entity receives an update location acknowledgement messagesent by the UDM entity.

The update location acknowledgement message includes subscriptioninformation, of the UE, that is subsequently used by the AMF to providea corresponding service included in the subscription information.

After the UE completes registration in the VPLMN and needs to establisha session, steps in FIG. 6A and FIG. 6B, FIG. 7A and FIG. 7B, and FIG.8A and FIG. 8B are performed.

FIG. 6A and FIG. 6B are a flowchart of a session establishment methodaccording to an embodiment of the present disclosure. As shown in FIG.6A and FIG. 6B, the method may include the following steps.

S201. A UE sends a first message to an AMF entity.

During session establishment, the UE needs to initiate the first messageto the AMF entity. The first message includes first information, firstnetwork slice selection information, and second network slice selectioninformation.

The first information includes information for requesting to establish aPDU session. In this embodiment of this application, the firstinformation may be a message, for example, a PDU session establishmentrequest message.

The first network slice selection information is used by the AMF entityto select a first SMF entity, for example, the first network sliceselection information may be S-NSSAI in a VPLMN. The second networkslice selection information is used by the AMF to select a second SMFentity, for example, the second network slice selection information maybe S-NSSAI in an HPLMN.

Both the first network slice selection information and the secondnetwork slice selection information are used to identify and determine anetwork slice. Both the first network slice selection information andthe second network slice selection information may include informationsuch as a type of a network slice and a name of a vendor that rents thenetwork slice.

S202. The AMF entity determines a first SMF entity based on the firstnetwork slice selection information, and determines a second SMF entitybased on the second network slice selection information.

It is assumed that the first network slice selection information isS-NSSAI in a VPLMN, and the second network slice selection informationis S-NSSAI in an HPLMN. After receiving the first message sent by theUE, the AMF entity determines a V-SMF entity, namely, the first SMFentity, based on the S-NSSAI in the VPLMN, and determines an H-SMFentity, namely, the second SMF entity, based on the S-NSSAI in theHPLMN. Then, the V-SMF entity selects a V-UPF entity, and the H-SMFentity selects an H-UPF entity, to continue session establishment.Finally, the AMF entity sends a second message to the UE. The secondmessage includes second information, and the second information includesPDU session establishment accept information.

S203. The UE receives a second message sent by the AMF entity.

After the session establishment method in this embodiment of thisapplication is used, the UE sends the S-NSSAI in the VPLMN and theS-NSSAI in the HPLMN to the AMF entity such that the AMF entity canaccurately determine S-NSSAI that should be used in the current VPLMNand S-NSSAI that should be used in the current HPLMN, to complete PDUsession establishment, and therefore the UE can perform communication.

Optionally, in this embodiment of this application, the first networkslice selection information may be S-NSSAI corresponding to a firstapplication in a VPLMN, and the second network slice selectioninformation may be S-NSSAI corresponding to the first application in anHPLMN.

The first application is any third-party application program appinstalled on the UE, for example, Facebook® or QQ.

Optionally, in this embodiment of this application, the AMF entity sendsthe second message to the UE, where the second message includes the PDUsession establishment accept information, and this step includes thefollowing steps.

The AMF entity sends a PDU session establishment response message to aRAN device.

The PDU session establishment response message includes the PDU sessionestablishment accept information, a first tunnel identifier, and firstaddress information.

The RAN device sends a radio resource control (RRC) message to the UE.

The RRC message includes the PDU session establishment acceptinformation, to notify the UE that session establishment is accepted.

Optionally, in this embodiment of this application, as shown in FIG. 6Aand FIG. 6B, after the AMF entity determines the first SMF entity basedon the first network slice selection information, and determines thesecond SMF entity based on the second network slice selectioninformation, the method may further include the following steps.

S204. The AMF entity sends a third message to the V-SMF entity.

The third message includes the PDU session establishment request messageand address information of the H-SMF entity. In this embodiment of thisapplication, the third message may be referred to as an N11 message orthe like. A specific name of the third message is not limited in thisembodiment of this application.

S205. The V-SMF entity determines a V-UPF entity based on the thirdmessage, and allocates, to a session that is being established, a firsttunnel identifier and first address information that are at a V-UPF endand a second tunnel identifier and second address information that areat the V-UPF end.

The first tunnel identifier and the first address information are atunnel identifier and address information that are at the V-UPF end andare used when a RAN device sends data to the V-UPF entity, namely, atunnel identifier and address information that are at the V-UPF end andare of an uplink (from the RAN device to the V-UPF entity) N3 tunnel.The second tunnel identifier and the second address information are atunnel identifier and address information that are at the V-UPF end andare used when the H-UPF entity sends data to the V-UPF entity, namely, atunnel identifier and address information that are at the V-UPF end andare of a downlink (from the H-UPF entity to the V-UPF entity) N9 tunnel.

The V-SMF entity determines the V-UPF entity based on the PDU sessionestablishment request message in the third message, and allocates thefirst tunnel identifier and the first address information that are atthe V-UPF end and the second tunnel identifier and the second addressinformation that are at the V-UPF end. The V-SMF entity sends a createsession message to the V-UPF entity, and the create session messageincludes information such as a packet detection rule and a reportingrule.

S206. The V-UPF receives a create session message sent by the V-SMFentity.

After receiving the create session message sent by the V-SMF entity, theV-UPF entity saves the information in the create session message, andreplies with a response message.

S207. The V-SMF entity sends a create session request message to theH-SMF entity.

The create session request message includes the second tunnel identifierand the second address information, namely, the tunnel identifier andthe address information that are at the V-UPF end and are used when theH-UPF entity transmits data to the V-UPF.

The V-SMF entity sends, based on the address information of the H-SMFentity included in the received third message sent by the AMF entity,the create session request message to the H-SMF entity corresponding tothe address information of the H-SMF entity.

S208. The H-SMF entity determines an H-UPF entity based on the createsession request message, and sends a create session message to the H-UPFentity.

The create session message includes the tunnel identifier and theaddress information that are the V-UPF end and are used when the H-UPFentity transmits data to the V-UPF, namely, the second tunnel identifierand the second address information.

After receiving the create session message, the H-UPF entity saves theinformation in the create session message, and replies with a responsemessage.

S209. The H-SMF entity sends a create session response message to theV-SMF entity.

The create session response message includes a tunnel identifier andaddress information that are at an H-UPF end and that are allocated bythe H-SMF entity to an uplink (from the V-UPF to the H-UPF) N9 tunnel.

The tunnel identifier and the address information that are at the H-UPFend and are of the uplink (from the V-UPF to the H-UPF) tunnel may beincluded in the create session response message, namely, the H-SMFentity sends the create session response message to the V-SMF entity,and the create session response message includes the tunnel identifierand the address information that are at the H-UPF end and are of theuplink (from the V-UPF to the H-UPF) tunnel.

S210. The AMF entity receives a fourth message.

The fourth message is sent by the V-SMF entity to the AMF entity, andincludes PDU session establishment accept information, and the firsttunnel identifier and the first address information, namely, the tunnelidentifier and the address information that are at the V-UPF end and areof the uplink (from the RAN device to the V-UPF entity) data sending N3tunnel. Namely, the fourth message includes the tunnel identifier andthe address information that are at the V-UPF end and are of the uplink(from the RAN device to the V-UPF entity) data sending N3 tunnel.

Optionally, after the UE receives the second message sent by the AMFentity, the method further includes:

S211. An RAN device sends a PDU session establishment response messageto the AMF entity.

The RAN device allocates a tunnel identifier and address informationthat are at a RAN end and are of a downlink (from the V-UPF entity tothe RAN device) data sending N3 tunnel, and sends the tunnel identifierand the address information to the AMF entity.

The RAN device sends, to the AMF entity using the PDU sessionestablishment response message, the allocated tunnel identifier andaddress information that are at the RAN end and are of the downlink(from the V-UPF entity to the RAN device) data sending N3 tunnel.

S212. The AMF entity sends the PDU session establishment responsemessage to the V-SMF entity.

The AMF entity needs to send, to the V-SMF entity, the received tunnelidentifier and address information that are at the RAN end and are ofthe N3 tunnel used when the V-UPF entity sends data to the RAN device.

The AMF entity sends the PDU session establishment response message tothe V-SMF entity, adds, into the PDU session establishment responsemessage, the tunnel identifier and the address information that are atthe RAN end and are of the N3 tunnel used when the V-UPF entity sendsdata to the RAN device, and sends the message to the V-SMF entity.

S213. The V-SMF entity sends a modify session message to V-UPF.

The modify session message includes the tunnel identifier and theaddress information that are at the RAN end and are of the N3 tunnelused when the V-UPF entity sends data to the RAN device, and a tunnelidentifier and address information that are at an H-UPF end and are ofan N9 tunnel used when the V-UPF sends data to H-UPF.

S214. The V-SMF entity responds to the V-AMF entity, to complete PDUsession establishment.

The V-SMF entity responds to the AMF entity, to complete PDU sessionestablishment.

In another embodiment of this application, as shown in FIG. 7A and FIG.7B, the first message in S201 may further include indicationinformation. The indication information is used to indicate that thefirst network slice selection information is S-NSSAI in an HPLMN, or theindication information is used to indicate that the first network sliceselection information is S-NSSAI in a VPLMN.

After receiving the first message sent by the UE, the AMF entitydetermines, based on a fact that the indication information indicatesthat the first network slice selection information is S-NSSAIcorresponding to a VPLMN, that the second network slice selectioninformation is S-NSSAI in an HPLMN, or the AMF entity determines, basedon a fact that the indication information indicates that the firstnetwork slice selection information is S-NSSAI in an HPLMN, that thesecond network slice selection information is S-NSSAI in a VPLMN. Inaddition, the AMF entity determines corresponding SMF entities based onthe first network slice selection information and the second networkslice selection information, namely, the AMF entity selects a V-SMFentity based on the S-NSSAI of the UE in the VPLMN, and selects an H-SMFentity based on the S-NSSAI of the UE in the HPLMN, to complete sessionestablishment. A session establishment process is the same as themethod/steps in steps S204 to S214 in FIG. 6A and FIG. 6B. For brevityof description, details are not described herein again.

Optionally, the indication information may be used to indicate that thesecond network slice selection information is S-NSSAI in a VPLMN orS-NSSAI in an HPLMN. The AMF entity may determine, based on theindication information, that the first network slice selectioninformation is S-NSSAI in an HPLMN or S-NSSAI corresponding to a VPLMN.

After the session establishment method provided in this embodiment ofthis application is used, the AMF entity may use the first network sliceselection information, the second network slice selection information,and the indication information that are sent by the UE to the AMFentity, namely, the S-NSSAI corresponding to the VPLMN, the S-NSSAI inthe HPLMN, and the information indicating S-NSSAI, to accuratelydetermine the V-SMF entity and the H-SMF entity, to further completesession establishment. Therefore, the following case is avoided: In aprocess in which the UE establishes a PDU session, the AMF entity cannotdetermine corresponding S-NSSAI of the UE, and cannot complete PDUsession establishment, and consequently the UE cannot performcommunication.

FIG. 8A and FIG. 8B show another session establishment method accordingto an embodiment of this application. As shown in FIG. 8A and FIG. 8B,the method may include the following steps.

S301. A UE sends a first message to an AMF entity.

During session establishment, the UE needs to initiate the first messageto the AMF entity. The first message includes first information, firstnetwork slice selection information, and indication information.

The first information includes information for requesting to establish aPDU session. In this embodiment of this application, the firstinformation may be a message, for example, a PDU session establishmentrequest message.

The first network slice selection information is used by the AMF entityto select an SMF entity. The indication information is used to indicatethat the first network slice selection information is S-NSSAI of the UEin a VPLMN, or is used to indicate that the first network sliceselection information is S-NSSAI of the UE in an HPLMN.

S302. The AMF entity determines, based on indication information, thatfirst network slice selection information is S-NSSAI of the UE in aVPLMN or first network slice selection information is S-NSSAI of the UEin an HPLMN, determines a first SMF entity based on the first networkslice selection information, determines second network slice selectioninformation based on the first network slice selection information andinformation about a correspondence between VPLMN S-NSSAI and HPLMNS-NSSAI, and selects a second SMF entity based on the second networkslice selection information.

It should be noted that, in this embodiment of this application, theinformation about the correspondence between VPLMN S-NSSAI and HPLMNS-NSSAI may be information about a one-to-one correspondence that isbetween VPLMN S-NSSAI and HPLMN S-NSSAI and that is defined according toa roaming protocol, or may be information about a one-to-manycorrespondence that is between VPLMN S-NSSAI and HPLMN S-NSSAI and thatis defined according to a roaming protocol.

When there is a one-to-one correspondence between VPLMN S-NSSAI andHPLMN S-NSSAI, for example, if an AMF entity pre-stores a table of aone-to-one mapping relationship between VPLMN S-NSSAI and HPLMN S-NSSAI,when the first network slice selection information is S-NSSAI in aVPLMN, the AMF entity may determine S-NSSAI in an HPLMN using themapping relationship table, and use the S-NSSAI as the second networkslice selection information. When there is a one-to-many correspondencebetween VPLMN S-NSSAI and HPLMN S-NSSAI, for example, if one piece ofVPLMN S-NSSAI corresponds to a plurality of pieces of HPLMN S-NSSAI,when the first network slice selection information is S-NSSAI in aVPLMN, the AMF entity may select one piece of HPLMN S-NSSAI based on asequence of priorities of the plurality of pieces of HPLMN S-NSSAI thatcorrespond to the VPLMN S-NSSAI, to further complete PDU sessionestablishment.

Optionally, the AMF entity may further select, based on a sessionattribute, HPLMN S-NSSAI corresponding to VPLMN S-NSSAI. For example,the AMF entity selects, based on a session type in a session attributeof the VPLMN S-NSSAI, HPLMN S-NSSAI whose session type is consistentwith the session type in the session attribute.

After determining the first SMF entity and the second SMF entity, theAMF entity further completes session establishment, and sends a secondmessage to the UE. The second message includes second information, andthe second information includes PDU session establishment acceptinformation.

S303. The UE receives a second message.

After the session establishment method in this embodiment of thisapplication is used, the UE sends, to the AMF entity, the S-NSSAI andthe information indicating that the S-NSSAI is the S-NSSAI of the UE inthe VPLMN or the HPLMN such that the AMF accurately determines a V-SMFentity and an H-SMF entity based on the message sent by the UE and theinformation about the correspondence between VPLMN S-NSSAI and HPLMNS-NSSAI, to further complete session establishment.

Optionally, in this embodiment of this application, the first networkslice selection information is S-NSSAI corresponding to a firstapplication. The first application is a third-party application programinstalled on the UE, for example, QQ or Facebook®.

In this embodiment of this application, the AMF entity determines theS-NSSAI corresponding to the VPLMN and the S-NSSAI corresponding to theHPLMN, and selects the V-SMF entity based on the S-NSSAI in the VPLMNand selects the H-SMF entity based on the S-NSSAI in the HPLMN, tocomplete session establishment. A session establishment process in stepsS304 to S314 is the same as the method/steps in steps S204 to S214 inFIG. 6A and FIG. 6B. For brevity of description, details are notdescribed herein again.

Optionally, in this embodiment of this application, before the UE sendsthe first message to the AMF entity, the method further includes:determining, by the UE, the network slice selection information, namely,the first network slice selection information.

A process of the foregoing step may include: if S-NSSAI corresponding tothe first application exists in a network slice selection policy in theVPLMN, determining, by the UE, the S-NSSAI as the first network sliceselection information; or if S-NSSAI corresponding to the firstapplication exists in a network slice selection policy in the HPLMN,determining, by the UE, the S-NSSAI as the first network slice selectioninformation.

The foregoing describes processes of the registration method and thesession establishment method. With reference to FIG. 9 to FIG. 14 , thefollowing describes in detail the terminal and the AMF that are providedin the embodiments of this application. It should be noted that, theterminal in the embodiments of this application may be referred to asUE.

FIG. 9 is a schematic structural diagram of a terminal according to anembodiment of this application. As shown in FIG. 9 , the terminal mayinclude a sending unit 410 and a receiving unit 420.

When the terminal roams from a home network to a visited PLMN, theterminal needs to perform network registration. In a registrationprocess, the sending unit 410 sends a registration request message to anAMF entity, and the registration request message includes a firstparameter that is used to request a network slice selection policy. Inthis embodiment of this application, the first parameter may be needNSSP indication information.

After receiving the registration request message sent by the terminal,the AMF entity obtains network slice selection information based on thefirst parameter in the registration request message, and sends aregistration accept message to the terminal. The registration acceptmessage includes the network slice selection information. Therefore,when establishing a PDU session, the terminal can accurately select,based on the network slice selection policy, S-NSSAI in a VPLMN or anHPLMN in which the terminal is located, to further complete PDU sessionestablishment.

Optionally, in this embodiment of this application, the terminal mayfurther include a processing unit configured to process related data.

FIG. 10 is a schematic structural diagram of a terminal according to anembodiment of this application. As shown in FIG. 10 , the terminal mayinclude a sending unit 510 and a receiving unit 520.

The sending unit 510 is configured to a first message to an AMF entity,where the first message includes first information, first network sliceselection information, and second network slice selection information.

The first information includes information for requesting to establish aPDU session. In this embodiment of this application, the firstinformation may be a message, for example, a PDU session establishmentrequest message.

The first network slice selection information is used by the AMF entityto select a first SMF entity, and the second network slice selectioninformation is used by the AMF entity to select a second SMF entity. Forexample, if the first network slice selection information is S-NSSAI ofthe terminal (or referred to as a UE) in a VPLMN, and the second networkslice selection information is S-NSSAI of the terminal (or referred toas a UE) in an HPLMN, the AMF selects a V-SMF entity, namely, the firstSMF entity, based on the S-NSSAI in the VPLMN, and the AMF entityselects an H-SMF entity, namely, the second SMF entity, based on theS-NSSAI in the HPLMN.

The receiving unit 520 is configured to receive a second message sent bythe AMF entity, where the second message includes second information,and the second information includes PDU session establishment acceptinformation.

After the terminal provided in this embodiment of this application isused, the terminal sends the S-NSSAI of the terminal in the VPLMN andthe S-NSSAI of the terminal in the HPLMN to the AMF entity such that theAMF accurately determines the V-SMF entity and the H-SMF entity based onthe two pieces of S-NSSAI, to further complete PDU sessionestablishment.

Optionally, in an embodiment of this application, the first networkslice selection information is S-NSSAI corresponding to a firstapplication in a VPLMN, and the second network slice selectioninformation is S-NSSAI corresponding to the first application in anHPLMN. The first application is a third-party application installed onthe terminal, for example, QQ or Facebook®.

Optionally, in another embodiment of this application, the first messagemay further include indication information, where the indicationinformation is used to indicate that the first network slice selectioninformation is S-NSSAI in an HPLMN, or the indication information isused to indicate that the first network slice selection information isS-NSSAI in a VPLMN.

In this embodiment of this application, the first message includes twopieces of S-NSSAI, and the indication information indicates one of thetwo pieces of S-NSSAI is S-NSSAI of the terminal in a VPLMN or S-NSSAIof the terminal in an HPLMN. After receiving the first message, the AMFentity determines, based on the indication information in the firstmessage, one of the two pieces of S-NSSAI is S-NSSAI of the terminal ina VPLMN, and the other piece of S-NSSAI is S-NSSAI of the terminal in anHPLMN, and selects the V-SMF entity based on the S-NSSAI in the VPLMNand selects the H-SMF entity based on the S-NSSAI in the HPLMN, tofurther complete PDU session establishment.

In addition, the terminal in this embodiment of this application mayfurther include a processing unit configured to perform relatedprocessing on data.

It should be noted that, in the embodiments of this application, theterminal provided in FIG. 10 and the terminal provided in FIG. 9 may bea same terminal, namely, the sending unit 510 and the receiving unit 520in FIG. 10 may be the sending unit 410 and the receiving unit 420 inFIG. 9 .

FIG. 11 shows a terminal according to an embodiment of this application.As shown in FIG. 11 , the terminal may include a sending unit 610 and areceiving unit 620.

The sending unit 610 is configured to a first message to an AMF entity,where the first message includes first information, network sliceselection information, and indication information.

The first information includes information for requesting to establish aPDU session. In this embodiment of this application, the firstinformation may be a message, for example, the first information is aPDU session establishment request message.

The network slice selection information is used by the AMF entity toselect an SMF entity. The indication information is used to indicatethat the network slice selection information is S-NSSAI in a VPLMN, oris used to indicate that the network slice selection information isS-NSSAI in a HPLMN.

Therefore, the AMF entity determines, based on the indicationinformation, that the network slice selection information is the S-NSSAIof the terminal in the VPLMN or the S-NSSAI of the terminal in theHPLMN, and further determines, based on the network slice selectioninformation, S-NSSAI of the terminal in an HPLMN or S-NSSAI of theterminal in a V-PLMN, and selects a V-SMF entity and an H-SMF entity.

The receiving unit 620 is configured to receive a second message sent bythe AMF entity, where the second message includes second information,and the second information includes PDU session establishment acceptinformation, to complete PDU session establishment.

Optionally, in this embodiment of this application, the network sliceselection information is S-NSSAI corresponding to a first application.The first application is a third-party application program installed onthe terminal, for example, QQ, Facebook®, or email.

Optionally, in this embodiment of this application, the terminal mayfurther include a processing unit 630. Before the terminal sends thefirst message to the AMF entity, the processing unit 630 further needsto determine the network slice selection information.

For example, the processing unit 630 performs the following processing:if S-NSSAI corresponding to the first application exists in a networkslice selection policy in the VPLMN, determining the S-NSSAI as thenetwork slice selection information; or if S-NSSAI corresponding to thefirst application exists in a network slice selection policy in theHPLMN, determining the S-NSSAI as the network slice selectioninformation.

It should be noted that, the terminal provided in FIG. 11 and theterminal provided in FIG. 9 may be a same terminal, namely, the sendingunit 610 and the receiving unit 620 in FIG. 11 are the sending unit 410and the receiving unit 420 in FIG. 9 .

FIG. 12 is a schematic structural diagram of an access and mobilitymanagement function entity according to an embodiment of thisapplication. As shown in FIG. 12 , the AMF entity may include areceiving unit 710, a processing unit 720, and a sending unit 730.

The receiving unit 710 is configured to receive a registration requestmessage sent by a terminal. The registration request message includes afirst parameter, and the first parameter is used to request a networkslice selection policy (NSSP). In this embodiment of this application,the first parameter may be need NSSP indication information.

The processing unit 720 is configured to obtain a network sliceselection policy based on the registration request message.

Optionally, in an embodiment of this application, the AMF entity mayobtain the NSSP of the terminal from a PCF entity.

For example, the sending unit 730 of the AMF entity sends a UE contextestablishment request message to the PCF entity, and the messageincludes the first parameter and UE identifier information, such as anIMSI. The PCF entity sends a UE context establishment response messageto the AMF entity based on the request from the AMF, and the messageincludes the NSSP of the UE and the UE identifier information.

The sending unit 730 is configured to send a registration accept messageto the terminal. The registration accept message includes the networkslice selection policy. In this way, in a process in which the terminalestablishes a PDU session, the AMF entity can accurately determine,based on the NSSP of the terminal, S-NSSAI in a VPLMN or an HPLMN inwhich the terminal is located, to further complete PDU sessionestablishment.

FIG. 13 is a schematic structural diagram of an access and mobilitymanagement function entity according to an embodiment of thisapplication. As shown in FIG. 13 , the AMF entity may include areceiving unit 810, a processing unit 820, and a sending unit 830.

The receiving unit 810 is configured to receive a first message sent bya terminal. The first message includes first information, first networkslice selection information, and second network slice selectioninformation.

The first information includes information for requesting to establish aPDU session. In this embodiment of this application, the firstinformation may be a message, for example, the first information is aPDU session establishment request message.

The processing unit 820 is configured to: determine a first SMF entitybased on the first network slice selection information; and determine asecond SMF entity based on the second network slice selectioninformation.

For example, if the first network slice selection information is S-NSSAIof the terminal in a VPLMN, and the second network slice selectioninformation is S-NSSAI of the terminal in an HPLMN, the AMF selects aV-SMF entity, namely, the first SMF entity, based on the S-NSSAI in theVPLMN, and the AMF entity selects an H-SMF entity, namely, the secondSMF entity, based on the S-NSSAI in the HPLMN.

The sending unit 830 is configured to send a second message to theterminal, where the second message includes second information, and thesecond information includes PDU session establishment acceptinformation, to complete PDU session establishment.

Optionally, in this embodiment of this application, the first networkslice selection information is S-NSSAI corresponding to a firstapplication in a VPLMN, and the second network slice selectioninformation is S-NSSAI corresponding to the first application in anHPLMN. The first application is a third-party application programinstalled on the terminal, for example, email, QQ, or Facebook®.

Optionally, in an embodiment of this application, the first message mayfurther include indication information that is used to indicate that thefirst network slice selection information is S-NSSAI in an HPLMN or thefirst network slice selection information is S-NSSAI in a VPLMN. Afterreceiving the first message, the AMF entity determines, based on theindication information in the first message, that each of the firstnetwork slice selection information and the second network sliceselection information that are included in the first message is S-NSSAIof the terminal in a VPLMN or S-NSSAI of the terminal in an HPLMN. Ifthe AMF entity determines, based on the indication information, that thefirst network slice selection information is S-NSSAI in a VPLMN, the AMFentity determines that the second network slice selection information isS-NSSAI in an HPLMN, and selects the H-SMF entity based on the S-NSSAIin the HPLMN and selects the V-SMF entity based on the S-NSSAI in theVPLMN, to further complete session establishment.

It should be noted that, the AMF entity provided in FIG. 13 and the AMFentity provided in FIG. 12 may be a same device, namely, the receivingunit 810, the processing unit 820, and the sending unit 830 in FIG. 13may be the receiving unit 710, the processing unit 720, and the sendingunit 730 in FIG. 12 .

FIG. 14 is a schematic structural diagram of another access and mobilitymanagement function entity according to an embodiment of thisapplication. As shown in FIG. 14 , the AMF entity may include areceiving unit 910, a processing unit 920, and a sending unit 930.

The receiving unit 910 is configured to receive a first message sent bya terminal. The first message includes first information, first networkslice selection information, and indication information.

The first information includes information for requesting to establish aPDU session. In this embodiment of this application, the firstinformation may be a message, for example, the first information is aPDU session establishment request message.

The indication information is used to indicate that the first networkslice selection information is S-NSSAI of the terminal in a VPLMN, or isused to indicate that the network slice selection information is S-NSSAIof the terminal in a HPLMN.

The processing unit 920 is configured to: determine, based on theindication information, that the first network slice selectioninformation is the S-NSSAI of the terminal in the VPLMN or the firstnetwork slice selection information is the S-NSSAI of the terminal inthe HPLMN; select a first SMF entity based on the first network sliceselection information; determine second network slice selectioninformation based on the first network slice selection information andinformation about a correspondence between VPLMN S-NSSAI and HPLMNS-NSSAI; and select a second SMF entity based on the second networkslice selection information.

The sending unit 930 is configured to send a second message to theterminal, where the second message includes second information, and thesecond information includes PDU session establishment acceptinformation, to complete PDU session establishment.

Optionally, in this embodiment of this application, the first networkslice selection information is S-NSSAI corresponding to a firstapplication.

The first application is a third-party application program installed onthe terminal, for example, QQ, Facebook®, or email.

It should be noted that, the AMF entity provided in FIG. 14 and the AMFentity provided in FIG. 13 may be a same device, namely, the receivingunit 910, the processing unit 920, and the sending unit 930 in FIG. 14may be the receiving unit 810, the processing unit 820, and the sendingunit 830 in FIG. 13 .

In addition, the terminal provided in FIG. 9 to FIG. 11 may furtherinclude a storage unit, and the AMF entity provided in FIG. 12 to FIG.14 may further include a storage unit, where the storage unit isconfigured to store a related instruction and related data.

It should further be noted that, in a process in which the terminalestablishes a PDU session, after the AMF entity receives the firstmessage sent by the terminal, namely, after the AMF entity receives thePDU session establishment request information, the AMF entity selectsthe V-SMF entity and the H-SMF entity based on the information includedin the first message, for example, the information included in the firstmessage in FIG. 10 , FIG. 11 , FIG. 13 , or FIG. 14 , to complete PDUsession establishment. A process thereof is the same as the method/stepsin steps S204 to S214 in FIG. 6A and FIG. 6B. For brevity ofdescription, details are not described herein again.

FIG. 15 shows a terminal according to an embodiment of this application.As shown in FIG. 15 , the terminal may include a transmitter 1010 and areceiver 1020.

The transmitter 1010 is configured to send a registration requestmessage to an AMF entity, where the registration request messageincludes a first parameter, and the first parameter is used to request anetwork slice selection policy.

The receiver 1020 is configured to receive a registration accept messagesent by the AMF entity, where the registration accept message includesthe network slice selection policy such that in a process in which theterminal subsequently establishes a PDU session, the terminal canaccurately determine corresponding S-NSSAI based on an NSSP in a currentVPLMN or HPLMN, and the following case is avoided: When the terminalestablishes a PDU session, the AMF entity cannot find S-NSSAIcorresponding to a network in which the terminal is located, and cannotcomplete PDU session establishment, and consequently the terminal cannotperform communication.

Optionally, in this embodiment of this application, the terminal mayfurther include a processor and a memory. The processor is configured toperform corresponding data processing by invoking an instruction fromthe memory. The memory is configured to store a correspondinginstruction and corresponding data.

FIG. 16 shows a terminal according to an embodiment of this application.As shown in FIG. 16 , the terminal may include a transmitter 1110 and areceiver 1120.

The transmitter 1110 is configured to send a first message to an AMFentity, where the first message includes first information, firstnetwork slice selection information, and second network slice selectioninformation, the first information includes information for requestingto establish a PDU session, the first network slice selectioninformation is used by the AMF entity to select a first SMF entity, andthe second network slice selection information is used by the AMF entityto select a second SMF entity.

The receiver 1120 is configured to receive a second message sent by theAMF entity, where the second message includes second information, andthe second information includes PDU session establishment acceptinformation.

After the terminal provided in this embodiment of this application isused, in a PDU session establishment process, the AMF entity canaccurately determine S-NSSAI, to complete PDU session establishment. Thefollowing case is avoided: When the terminal establishes a PDU session,the AMF entity cannot find S-NSSAI corresponding to a network in whichthe terminal is located, and cannot complete PDU session establishment,and consequently the terminal cannot perform communication.

Optionally, in an embodiment of this application, the first networkslice selection information may be S-NSSAI corresponding to a firstapplication in a VPLMN, and the second network slice selectioninformation is S-NSSAI corresponding to the first application in aHPLMN.

Optionally, in another embodiment of this application, the first messagefurther includes indication information, where the indicationinformation is used to indicate that the first network slice selectioninformation is S-NSSAI in a VPLMN, or the indication information is usedto indicate that the first network slice selection information isS-NSSAI in a HPLMN. Therefore, after receiving the first message, theAMF entity determines the first network slice selection information andthe second network slice selection information based on the indicationinformation in the first message, to further complete PDU sessionestablishment.

In addition, optionally, the terminal provided in this embodiment ofthis application may further include a processor and a memory. Thememory is configured to store a corresponding instruction andcorresponding data such that the processor invokes the instruction fromthe memory and performs corresponding processing on data.

FIG. 17 shows a terminal according to an embodiment of this application.As shown in FIG. 17 , the terminal may include a transmitter 1210 and areceiver 1220.

The transmitter 1210 is configured to send a first message to an AMFentity, where the first message includes first information, networkslice selection information, and indication information, the firstinformation includes information for requesting to establish a PDUsession, the network slice selection information is used by the AMFentity to select an SMF entity, and the indication information is usedto indicate that the network slice selection information is S-NSSAI ofthe terminal in a VPLMN, or is used to indicate that the network sliceselection information is S-NSSAI of the terminal in a HPLMN.

The receiver 1220 is configured to receive a second message sent by theAMF entity, where the second message includes second information, andthe second information includes PDU session establishment acceptinformation.

After the terminal provided in this embodiment of this application isused, in a PDU session establishment process, the AMF entity canaccurately determine S-NSSAI, to complete PDU session establishment. Thefollowing case is avoided: When the terminal establishes a PDU session,the AMF entity cannot find S-NSSAI corresponding to a network in whichthe terminal is located, and cannot complete PDU session establishment,and consequently the terminal cannot perform communication.

Optionally, in an embodiment of this application, the network sliceselection information is S-NSSAI corresponding to a first application.

Optionally, in another embodiment of this application, the terminalfurther includes a processor 1230 configured to determine the networkslice selection information.

Optionally, in an embodiment, that the processor 1230 determines thenetwork slice selection information includes: if S-NSSAI correspondingto the first application exists in a network slice selection policy inthe VPLMN, determining, by the terminal, the S-NSSAI as the networkslice selection information; or if S-NSSAI corresponding to the firstapplication exists in a network slice selection policy in the HPLMN,determining, by the terminal, the S-NSSAI as the network slice selectioninformation.

Similarly, optionally, the terminal provided in this embodiment of thisapplication may further include a processor and a memory. The memory isconfigured to store a corresponding instruction and corresponding datasuch that the processor invokes the instruction from the memory andperforms corresponding processing on data.

FIG. 18 shows an AMF entity according to an embodiment of thisapplication. As shown in FIG. 18 , the AMF entity may include a receiver1310, a processor 1320, and a transmitter 1330.

The receiver 1310 is configured to receive a registration requestmessage sent by a terminal, where the registration request messageincludes a first parameter, and the first parameter is used to request anetwork slice selection policy.

The processor 1320 is configured to obtain a network slice selectionpolicy based on the registration request message.

The transmitter 1330 is configured to send a registration accept messageto the terminal, where the registration accept message includes thenetwork slice selection policy.

A network slice selection policy in a network in which the terminal islocated is obtained using the first parameter sent by the terminal tothe AMF entity such that when a PDU session is subsequently established,corresponding S-NSSAI is accurately determined based on the networkslice selection policy, and the following case is avoided: When theterminal establishes a PDU session, the AMF entity cannot find S-NSSAIcorresponding to the network in which the terminal is located, andcannot complete PDU session establishment, and consequently the terminalcannot perform communication.

Optionally, in an embodiment of this application, that the processorobtains a network slice selection policy based on the registrationrequest message includes: sending, by the transmitter 1330, a firstmessage to a PCF entity, where the first message includes the firstparameter; and receiving, by the receiver 1310, a second message sent bythe PCF entity, where the second message includes the network sliceselection policy.

Optionally, the AMF provided in this embodiment of this application mayfurther include a memory. The memory is configured to store acorresponding instruction and corresponding data such that the processorinvokes the instruction from the memory and performs correspondingprocessing on data.

FIG. 19 shows an AMF entity according to an embodiment of thisapplication. As shown in FIG. 19 , the AMF entity may include a receiver1410, a processor 1420, and a receiver 1430.

The receiver 1410 is configured to receive a first message sent by aterminal, where the first message includes first information, firstnetwork slice selection information, and second network slice selectioninformation, and the first information includes information forrequesting to establish a PDU session.

The processor 1420 is configured to: determine a first SMF entity basedon the first network slice selection information; and determine a secondSMF entity based on the second network slice selection information.

The transmitter 1430 is configured to send a second message to theterminal, where the second message includes second information, and thesecond information includes PDU session establishment acceptinformation.

In this way, in a process in which the terminal subsequently establishesa PDU session, the terminal can accurately determine correspondingS-NSSAI based on an NSSP in a current VPLMN or HPLMN, and the followingcase is avoided: When the terminal establishes a PDU session, the AMFentity cannot find S-NSSAI corresponding to a network in which theterminal is located, and cannot complete PDU session establishment, andconsequently the terminal cannot perform communication.

Optionally, in an embodiment of this application, the first networkslice selection information is S-NSSAI corresponding to a firstapplication in a VPLMN, and the second network slice selectioninformation is S-NSSAI corresponding to the first application in aHPLMN.

In another embodiment of this application, the first message furtherincludes indication information, where the indication information isused to indicate that the first network slice selection information isS-NSSAI in a VPLMN, or the indication information is used to indicatethat the first network slice selection information is S-NSSAI in aHPLMN. Therefore, after receiving the first message, the AMF entitydetermines the first network slice selection information and the secondnetwork slice selection information based on the indication informationin the first message, to further complete PDU session establishment.

In addition, optionally, the AMF entity provided in this embodiment ofthis application may further include a memory. The memory is configuredto store a corresponding instruction and corresponding data such thatthe processor invokes the instruction from the memory and performscorresponding processing on data.

FIG. 20 shows an AMF entity according to an embodiment of thisapplication. As shown in FIG. 20 , the AMF entity may include a receiver1510, a processor 1520, and a transmitter 1530.

The receiver 1510 is configured to receive a first message sent by aterminal, where the first message includes first information, firstnetwork slice selection information, and indication information, thefirst information includes information for requesting to establish a PDUsession, and the indication information is used to indicate that thefirst network slice selection information is S-NSSAI of the terminal ina VPLMN, or is used to indicate that the network slice selectioninformation is S-NSSAI of the terminal in a HPLMN.

The processor 1520 is configured to: determine, based on the indicationinformation, that the first network slice selection information is theS-NSSAI of the terminal in the VPLMN or the first network sliceselection information is the S-NSSAI of the terminal in the HPLMN;select a first SMF entity based on the first network slice selectioninformation; determine second network slice selection information basedon the first network slice selection information and information about acorrespondence between VPLMN S-NSSAI and HPLMN S-NSSAI; and select asecond SMF entity based on the second network slice selectioninformation.

The transmitter 1530 is configured to send a second message to theterminal, where the second message includes second information, and thesecond information includes PDU session establishment acceptinformation.

After the solution provided in this embodiment of this application isused, the AMF entity can accurately determine to-be-used S-NSSAI basedon the first network slice selection information and the indicationinformation, to complete PDU session establishment.

In an embodiment of this application, the first network slice selectioninformation is S-NSSAI corresponding to a first application.

In addition, the AMF entity provided in this embodiment of thisapplication may further include a processor and a memory. The memory isconfigured to store a corresponding instruction and corresponding datasuch that the processor invokes the instruction from the memory andperforms corresponding processing on data.

An embodiment of this application provides a computer program productincluding an instruction, and when the instruction runs on a computer,the methods/steps in FIG. 5 to FIG. 8A and FIG. 8B are performed.

An embodiment of this application provides a computer readable storagemedium configured to store an instruction, and when the instruction isexecuted on a computer, the methods/steps in FIG. 5 to FIG. 8A and FIG.8B are performed.

All or some of the foregoing embodiments of the present disclosure maybe implemented using software, hardware, firmware, or any combinationthereof. When software is used to implement the embodiments, all or someof the embodiments may be implemented in a form of a computer programproduct. The computer program product includes one or more computerinstructions. When the computer program instructions are loaded andexecuted on the computer, all or some of the procedures or functionsaccording to the embodiments of the present disclosure are generated.The computer may be a general-purpose computer, a dedicated computer, acomputer network, or another programmable apparatus. The computerinstructions may be stored in a computer-readable storage medium or maybe transmitted from a computer-readable storage medium to anothercomputer-readable storage medium. For example, the computer instructionsmay be transmitted from a website, computer, server, or data center toanother website, computer, server, or data center in a wired (forexample, a coaxial cable, an optical fiber, or a digital subscriber line(DSL)) or wireless (for example, infrared, radio, or microwave) manner.The computer-readable storage medium may be any usable medium accessibleby a computer, or may be a data storage device, such as a server or adata center, integrating one or more usable media. The usable medium maybe a magnetic medium (for example, a floppy disk, a hard disk, or amagnetic tape), an optical medium (for example, digital video disc(DVD)), a semiconductor medium (for example, a solid-state disk orsolid-state drive (SSD)), or the like.

The foregoing descriptions are only examples of implementations of thisapplication, but are not intended to limit the protection scope of thisapplication. Any variation or replacement readily figured out by aperson skilled in the art within the technical scope disclosed in thisapplication shall fall within the protection scope of this application.Therefore, the protection scope of this application shall be subject tothe protection scope of the claims.

What is claimed is:
 1. A session establishment method, comprises:receiving, by an access and mobility management function entity from aterminal, a message comprising first network slice selectioninformation, second network slice selection information, and firstinformation for requesting to establish a protocol data unit session;determining, by the access and mobility management function entity, afirst session management control function entity in a visited publicland mobile network (VPLMN) based on the first network slice selectioninformation; determining, by the access and mobility management functionentity, a second session management control function entity in a homepublic land mobile network (HPLMN) based on the second network sliceselection information; sending, by the access and mobility managementfunction entity to the first session management control function entity,a message comprising the first information; and receiving, by the firstsession management control function entity, the message comprising thefirst information from the access and mobility management functionentity.
 2. The session establishment method of claim 1, wherein thesecond message comprising e first information further comprises secondinformation of the second session management control function entity. 3.The session establishment method of claim 2, wherein the secondinformation comprises an identity of the second session managementcontrol function entity.
 4. The session establishment method of claim 1,further comprising: selecting, by the first session management controlfunction entity, a first user plane function entity in the VPLMN;sending, by the first session management control function entity, arequest message to the second session management control functionentity, wherein the request message comprises first tunnel informationof a tunnel between the first user plane function entity and a seconduser plane function entity in the HPLMN, and wherein the first tunnelinformation is at the first user plane function entity; and receiving,by the first session management control function entity, a responsemessage from the second session management control function entity,wherein the response message comprises second tunnel information of thetunnel, and wherein the second t gel information is at the second userplane function entity.
 5. The session establishment method of claim 4,further comprising, sending, by the first session management controlfunction entity to the first user plane function entity, the firsttunnel information, the second tunnel information, and third tunnelinformation of the tunnel, and wherein the third tunnel information isat a radio access network.
 6. The session establishment method of claim4, further comprising: sending, by the first session management controlfunction entity, the first tunnel information to the access and mobilitymanagement function entity; and sending, by the access and mobilitymanagement function entity, the first tunnel information to a radioaccess network.
 7. The session establishment method of claim 1, furthercomprising: receiving, by the access and mobility management functionentity from the first session management control function entity,information indicating that establishment of the protocol data unitsession is accepted; and sending, by the access and mobility managementfunction entity to the terminal, information indicating that theestablishment of the protocol data unit session is accepted.
 8. Thesession establishment method of claim 1, wherein the first network sliceselection information comprises first single network slice selectionassistance information for the VPLMN, and wherein the second networkslice selection information comprises second single network sliceselection assistance information for the HPLMN.
 9. The sessionestablishment method of claim 8, wherein the first single network sliceselection assistance information corresponds to an application.
 10. Thesession establishment method of claim 9, wherein the second singlenetwork slice selection assistance information corresponds to theapplication.
 11. A network system, comprising: a first sessionmanagement control function entity in a visited public land mobilenetwork (VPLMN), wherein the first session management control functionentity is configured to receive a message comprising first informationfor requesting to establish a protocol data unit session; and an accessand mobility management function entity configured to: receive, from aterminal, a message comprising first network slice selectioninformation, second network slice selection information, and the firstinformation; determine the first session management control functionentity based on the first network slice selection information; determinea second session management control function entity in a home publicland mobile network (HPLMN) based on the second network slice selectioninformation; and send the message comprising the first information tothe first session management control function entity.
 12. The networksystem of claim 11, wherein the message comprising the first informationfurther comprises second information of the second session managementcontrol function entity.
 13. The network system of claim 12, wherein thesecond information comprises an identity of the second sessionmanagement control function entity.
 14. The network system of claim 11,further comprising a first user plane function entity in the VPLMN,wherein the first session management control function entity is furtherconfigured to: select the first user plane function entity; send arequest message to the second session management control functionentity, wherein the request message comprises first tunnel informationof a tunnel between the first user plane function entity and a seconduser plane function entity in the HPLMN, and wherein the first tunnelinformation is at the first user plane function entity; and receive aresponse message from the second session management control functionentity, wherein the response message comprises second tunnel informationof the tunnel and wherein the second tunnel information is at the seconduser plane function entity.
 15. The network system of claim 14, whereinthe first session management control function entity is furtherconfigured to send, to the first user plane function entity, the firsttunnel information, the second tunnel information, and third tunnelinformation of the tunnel, and wherein the third tunnel information isat a radio access network.
 16. The network system of claim 14, whereinthe first session management control function entity is furtherconfigured to send the first tunnel information to the access andmobility management function entity, and wherein the access and mobilitymanagement function entity is further configured to send the firsttunnel information to a radio access network.
 17. The network system ofclaim 11, wherein the access and mobility management function entity isfurther configured to: receive from the first session management controlfunction entity, information indicating that establishment of theprotocol data unit session is accepted; and send, to the terminal,information indicating that the establishment of the protocol data unitsession is accepted.
 18. The network system of claim 11, wherein thefirst network slice selection information comprises first single networkslice selection assistance information for the VPLMN, and wherein thesecond network slice selection information comprises second singlenetwork slice selection assistance information for the HPLMN.
 19. Thenetwork system of claim 18, wherein the first single network sliceselection assistance information corresponds to an application.
 20. Thenetwork system of claim 19, wherein the second single network sliceselection assistance information corresponds to the application.